Vaccination of influenza a virus decreases transmission rates in pigs

Romagosa, Anna; Allerson, Matt; Gramer, Marie; Joo, Han Soo; Deen, John; Detmer, Susan; Torremorell, Montserrat

R 0 of influenza virus has been estimated previously in chickens and horses. R 0 was estimated at 1.6 to 3.5 and at 208 for H5N1 and H7N7 avian influenza strains respectively, and at 10.18 for an equine influenza strain [28, [30] [31] [32] . In these studies R was reduced to 0 in chickens vaccinated with an inactivated H5N2 strain against an H5N1, and it was also 0 in chickens vaccinated with two inactivated H7N1 and H7N3 strains against an H7N7 avian flu virus. In contrast, a recent study reported that transmission of a H5N1 was not affected by vaccination of broiler chickens and suggested that this might have been due to the interference of maternal immunity [33] . In horses, R was reduced to 2.4 for a homologously vaccinated population and to 4.9 for a heterologously vaccinated population. To our knowledge this is the first study that has calculated R 0 for influenza A virus in pigs and R 0 is within the reported values for influenza in other species. In addition, results from our study also suggest that vaccination of pigs can be used to reduce their level of susceptibility, although a degree of virus spread can still take place in populations with immunity.